U.S. patent number 6,572,683 [Application Number 09/991,349] was granted by the patent office on 2003-06-03 for substance separation structure and method of preparing the same.
This patent grant is currently assigned to Sumitomo Electric Industries, Ltd.. Invention is credited to Takeshi Hikata, Nobuyuki Okuda, Takashi Uemura, Kentaro Yoshida.
United States Patent |
6,572,683 |
Yoshida , et al. |
June 3, 2003 |
Substance separation structure and method of preparing the same
Abstract
A substance separation structure comprises a base material
including a porous material having a continuous hole with an
opening of the hole formed on at least one surface, a porous layer,
formed to fill up the opening, having a hole smaller than the hole
of the base material and a permeable membrane of not more than 1
.mu.m in thickness formed on at least one surface of the base
material formed with the porous layer to selectively permeate ions
or neutral elements or molecules, and the surface roughness of at
least one surface of the base material formed with the porous layer
is not more than 0.3 .mu.m in Rmax. The surface of the base
material is polished with abrasive grains containing a porous
material so that the opening of the base material can be filled up
with the porous layer, and the permeable membrane is formed by ion
plating.
Inventors: |
Yoshida; Kentaro (Itami,
JP), Hikata; Takeshi (Itami, JP), Okuda;
Nobuyuki (Itami, JP), Uemura; Takashi (Itami,
JP) |
Assignee: |
Sumitomo Electric Industries,
Ltd. (Osaka, JP)
|
Family
ID: |
26604520 |
Appl.
No.: |
09/991,349 |
Filed: |
November 20, 2001 |
Foreign Application Priority Data
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Nov 24, 2000 [JP] |
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2000-357405 |
Oct 12, 2001 [JP] |
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2001-314754 |
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Current U.S.
Class: |
96/11; 55/524;
55/DIG.5; 95/56 |
Current CPC
Class: |
B01D
53/228 (20130101); B01D 67/0072 (20130101); B01D
69/10 (20130101); B01D 69/12 (20130101); B01D
71/02 (20130101); B01D 71/022 (20130101); B01D
71/025 (20130101); C01B 3/505 (20130101); C01B
2203/0405 (20130101); C01B 2203/047 (20130101); C01B
2203/0475 (20130101); Y10S 55/05 (20130101); B01D
2325/04 (20130101); B01D 2325/20 (20130101) |
Current International
Class: |
B01D
53/22 (20060101); B01D 69/00 (20060101); B01D
69/10 (20060101); B01D 71/00 (20060101); B01D
71/02 (20060101); C01B 3/50 (20060101); C01B
3/00 (20060101); B01D 053/22 (); B01D 071/02 () |
Field of
Search: |
;95/45,55,56 ;96/4.11
;55/524,DIG.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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05085702 |
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Apr 1993 |
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JP |
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08071385 |
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Mar 1996 |
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JP |
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11267477 |
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Oct 1999 |
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JP |
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2000237561 |
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Sep 2000 |
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JP |
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WO 00/32512 |
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Jun 2000 |
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WO |
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Primary Examiner: Spitzer; Robert H.
Attorney, Agent or Firm: Fasse; W. F. Fasse; W. G.
Claims
What is claimed is:
1. A substance separation structure comprising: a base material
including a porous material having a continuous hole with an
opening of said hole formed on at least one surface; a porous
layer, formed to fill up said opening formed on said at least one
surface of said base material, having a hole smaller than said hole
of said base material; and a permeable membrane of not more than 1
.mu.m in thickness formed on said at least one surface of said base
material formed with said porous layer to selectively permeate ions
or neutral elements or molecules, wherein the surface roughness of
said at least one surface of said base material formed with said
porous layer is not more than 0.3 .mu.m in Rmax.
2. The substance separation structure according to claim 1, wherein
the ratio (Tb/Ta) of the mean thickness Tb of a portion of said
porous layer formed on said surface of said base material outside
said hole of said base material to the mean thickness Ta of a
portion of said porous layer formed in said hole of said base
material is at least 0 and not more than 1.
3. The substance separation structure according to claim 1, wherein
said porous material forming said base material is at least one
material selected from a group consisting of ceramics, a metal and
a complex of said ceramics and said metal.
4. The substance separation structure according to claim 1, wherein
said porous material forming said base material is porous silicon
nitride having porosity of at least 30% and not more than 70%.
5. The substance separation structure according to claim 1, wherein
said porous material forming said base material includes at least
one material selected from a group consisting of iron and nickel,
and has porosity of at least 60% and not more than 95%.
6. The substance separation structure according to claim 1, wherein
said permeable membrane is made of a metal, an alloy or a compound
containing at least one material selected from a group consisting
of palladium, platinum, gold, silver, vanadium, niobium, tantalum
and zirconium.
7. The substance separation structure according to claim 6, wherein
said permeable membrane is formed by a single layer or a plurality
of layers.
8. The substance separation structure according to claim 1, wherein
said permeable membrane is made of a compound having a zeolite
structure or a perovskite structure.
9. The substance separation structure according to claim 1, wherein
the surface roughness of said at least one surface of said base
material not yet formed with said porous layer is not more than 0.3
.mu.m in Rmax.
10. The substance separation structure according to claim 1,
wherein the surface roughness of said at least one surface of said
base material formed with said porous layer and said permeable
membrane is not more than 0.3 .mu.m in Rmax.
11. A method of preparing a substance separation structure
comprising steps of: polishing a surface of a base material
including a porous material having a continuous hole with an
opening of said hole formed on at least one surface with abrasive
grains containing a porous material to be capable of filling up
said opening with a porous layer; and forming a permeable membrane
of not more than 1 .mu.m in thickness by plating or ion plating on
said surface of said base material formed with said porous layer by
said polishing.
12. The method of preparing a substance separation structure
according to claim 11, wherein said porous material forming said
base material is at least one material selected from a group
consisting of ceramics, a metal and a complex of said ceramics and
said metal.
13. The method of preparing a substance separation structure
according to claim 11, wherein said abrasive grains containing said
porous material contain at least one material selected from a group
consisting of porous aluminum oxide and titanium oxide.
14. The method of preparing a substance separation structure
according to claim 11, wherein the average diameter of said
abrasive grains containing said porous material is smaller than the
average diameter of said opening formed on said at least one
surface of said base material.
15. The method of preparing a substance separation structure
according to claim 11, wherein said ion plating is arc ion plating.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a substance separation
structure and a method of preparing the same, and more
specifically, it relates to a substance separation structure
provided with a permeable membrane formed on a porous base material
having continuous holes and a method of preparing the same.
2. Description of the Prior Art
A gas permeation membrane is put into practice in the field of
oxygen enrichment, nitrogen enrichment, carbon dioxide separation,
hydrogen separation and the like. An oxygen enrichment membrane or
a nitrogen enrichment membrane concentrating oxygen or nitrogen
contained in the air is employed for combustion or medical
application. A carbon dioxide separation membrane separating
methane and carbon dioxide contained in natural gas from each other
is employed for recovering carbon dioxide. A hydrogen separation
membrane is used for separating and recovering gaseous hydrogen
employed for desulfurizing petroleum.
Gaseous hydrogen, employed as the fuel for a fuel cell or the like,
is industrially prepared by denaturation of gaseous fuel or the
like. According to the denaturation of gaseous fuel, for example,
gaseous hydrogen is prepared by reforming steam, while the reformed
gas contains carbon monoxide, carbon dioxide and the like as
subcomponents in addition to the main component of hydrogen. When
the reformed gas is applied to the fuel for a fuel cell as such,
for example, the performance of the cell is deteriorated.
Therefore, the reformed gas must be purified for removing the
subcomponents other than hydrogen and obtaining high-purity gaseous
hydrogen. The reformed gas may be purified by a method utilizing
the characteristic of a hydrogen-permeable membrane selectively
permeating only hydrogen.
Japanese Patent Laying-Open No. 11-267477 (1999) proposes a method
of forming a hydrogen-permeable metal film such as a Pd film or an
Nb film of about 0.1 to 20 .mu.m in thickness on a surface of a
porous support of stainless steel or ceramics such as alumina or
silicon nitride by ion plating, in order to prepare a
hydrogen-permeable membrane having no pinholes.
The hydrogen permeability of such a hydrogen-permeable membrane is
in inverse proportion to the thickness thereof, and hence the
thickness of the hydrogen-permeable membrane must be reduced to the
utmost in order to improve the hydrogen permeability. When a
hydrogen-permeable membrane of not more than 1 .mu.m in thickness
is formed on a surface of a porous base material by ion plating,
however, it is impossible to form a dense membrane having no
pinholes. Therefore, a hydrogen-permeable membrane sufficiently
improved in hydrogen permeability cannot be prepared.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a substance
separation structure capable of forming a hydrogen-permeable
membrane of not more than 1 .mu.m in thickness on a surface of a
porous base material as a dense membrane having no pinholes with
high hydrogen permeability and durability, and a method of
preparing the same.
The inventor has made various studies on membrane forming methods,
to find out that a dense membrane having no pinholes can be
prepared by polishing a surface of a porous base material with
abrasive grains containing a porous material and thereafter forming
a permeable membrane.
On the basis of this recognition, a substance separation structure
according to an aspect of the present invention comprises a base
material including a porous material having a continuous hole with
an opening of the hole formed on at least one surface, a porous
layer, formed to fill up the opening formed on at least one surface
of the base material, having a hole smaller than the hole of the
base material, and a permeable membrane of not more than 1 .mu.m in
thickness formed on at least one surface of the base material
formed with the porous layer to selectively permeate ions or
neutral elements or molecules, while the surface roughness of at
least one surface of the base material formed with the porous layer
is not more than 0.3 .mu.m in Rmax.
In the substance separation structure according to the present
invention, the surface of the base material is flattened to the
surface roughness of not more than 0.3 .mu.m in Rmax while the
opening of the hole formed on the surface of the base material is
filled up with the porous layer, whereby the permeable membrane of
not more than 1 .mu.m in thickness can be formed on the surface of
the base material in a dense state with no pinholes. Thus,
permeability of the permeable membrane can be improved.
In the substance separation structure according to the present
invention, the ratio (Tb/Ta) of the mean thickness Tb of a portion
of the porous layer formed on the surface of the base material
outside the hole of the base material to the mean thickness Ta of a
portion of the porous layer formed in the hole of the base material
is set to at least 0 and not more than 1, thereby improving
adhesion between the permeable membrane and the surface of the base
material. Thus, durability of the substance separation structure
can be improved.
Preferably, the porous material forming the base material is at
least one material selected from a group consisting of ceramics, a
metal and a complex of the ceramics and the metal.
More preferably, the porous material forming the base material is
porous silicon nitride having porosity of at least 30% and not more
than 70%.
Further preferably, the porous material forming the base material
includes at least one material selected from a group consisting of
iron and nickel, and has porosity of at least 60% and not more than
95%.
In the substance separation structure according to the present
invention, the permeable membrane may not be porous. Preferably,
the permeable membrane is made of a metal, an alloy or a compound
containing at least one material selected from a group consisting
of palladium (Pd), platinum (Pt), gold (Au), silver (Ag), niobium
(Nb), tantalum (Ta), vanadium (V) and zirconium (Zr). More
preferably, the permeable membrane is formed by a single layer or a
plurality of layers. Further preferably, the permeable membrane is
made of a compound having a zeolite structure or a perovskite
structure.
Preferably, the surface roughness of at least one surface of the
base material not yet formed with the porous layer is not more than
0.3 .mu.m in Rmax. More preferably, the surface roughness of at
least one surface of the base material formed with the porous layer
and the permeable membrane is not more than 0.3 .mu.m in Rmax.
A method of preparing a substance separation structure according to
another aspect of the present invention comprises steps of
polishing a surface of a base material including a porous material
having a continuous hole with an opening of the hole formed on at
least one surface with abrasive grains containing a porous material
to be capable of filling up the opening with a porous layer and
forming a permeable membrane of not more than 1 .mu.m in thickness
by plating or ion plating on the surface of the base material
formed with the porous layer by the polishing.
Preferably in the method according to the present invention, the
porous material forming the base material is at least one material
selected from a group consisting of ceramics, a metal and a complex
of the ceramics and the metal.
Preferably, the abrasive grains containing the porous material
contain at least one material selected from a group consisting of
porous aluminum oxide and titanium oxide. More preferably, the
average diameter of the abrasive grains containing the porous
material is smaller than the average diameter of the opening formed
on at least one surface of the base material.
In the method according to the present invention, arc ion plating
is preferably employed as the ion plating.
The foregoing and other objects, features, aspects and advantages
of the present invention will become more apparent from the
following detailed description of the present invention when taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view showing a substance separation
structure according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIG. 1, a substance separation structure 10 according
to the present invention comprises a base material 1, a porous
layer 2 formed to fill up openings 11 provided on at least one
surface of the base material 1 and a permeable membrane 3 of not
more than 1 .mu.m in thickness provided on at least the surface of
the base material 1 formed with the porous layer 2. The base
material 1 consists of a porous material having a number of
continuous holes (not shown) communicating with the openings 11,
and the porous layer 2 has holes (not shown) smaller than those of
the base material 1. The permeable membrane 3 is formed to
selectively permeate ions or neutral elements or molecules. The
surface roughness of at least the surface of the base material 1
formed with the porous layer 2 is not more than 0.3 .mu.m in
Rmax.
In an embodiment of the substance separation structure according to
the present invention, a permeable membrane of not more than 1
.mu.m in thickness is formed on a surface of a porous silicon
nitride base material flattened to have surface roughness of not
more than 0.3 .mu.m in Rmax by polishing with abrasive grains
containing a porous material. The abrasive grains containing a
porous material are preferably prepared from those containing
grains of .gamma.-aluminum oxide (.gamma.-Al.sub.2 O.sub.3) grains.
It is preferable to employ aluminum oxide abrasive grains having an
average diameter smaller than the average diameter of openings of
holes formed on the surface of the silicon nitride base material.
The material for the permeable membrane can be prepared from any of
metals such as palladium, platinum, gold, silver, vanadium,
niobium, tantalum and zirconium or an alloy or a compound
containing any of these metals.
On the flattened surface of the silicon nitride base material, the
porous aluminum oxide layer is formed on the portions of the holes.
The porous aluminum oxide layer consists of portions A formed in
the holes of the silicon nitride base material and portions B
formed on the surface of the silicon nitride base material outside
the holes, and the ratio (Tb/Ta) of the mean thickness Tb of the
portions B to the mean thickness Ta of the portions A is at least 0
and not more than 1. High adhesion is attained between the
permeable membrane formed on the surface of the base material and
the base material. Therefore, the permeable membrane is not
separated from the base material but maintains a dense state with
no pinholes when purifying hydrogen-containing gas. Thus, gas other
than hydrogen can be remarkably inhibited from passing through the
permeable membrane, and high-purity gaseous hydrogen can be
obtained.
The permeable membrane is formed on the surface of the porous base
material by plating or ion plating. While ion plating includes
various types of methods and any method is applicable to the
present invention, arc ion plating (arc discharge ion plating) is
particularly preferably employed.
While a palladium film, for example, has excellent hydrogen
permeability for serving as the permeable membrane, (100) planes of
palladium crystals exhibit lower hydrogen permeability than the
remaining crystal planes. When a palladium film is so formed as to
orient palladium crystals on (111) planes, superior hydrogen
permeability can be attained as compared with a palladium film
having no such orientation. According to the inventive method, a
palladium film is formed on a surface, flattened by polishing with
abrasive grains containing a porous material, of a porous base
material having continuous holes by arc ion plating with
application of a bias voltage so that palladium crystals are
oriented in (111) planes, whereby excellent hydrogen permeability
can be attained.
Porous silicon nitride employed for the base material of the
inventive substance separation structure preferably has network
hole portions formed by columnar .beta.-Si.sub.3 N.sub.4 crystal
grains intertwined with each other. The porosity of the porous
silicon nitride is preferably within the range of 30 to 70%,
particularly preferably within the range of 40 to 50%. Further, the
bending strength of the porous silicon nitride base material is
preferably within the range of 30 to 450 MPa, and particularly
preferably within the range of 200 to 450 MPa.
The hydrogen permeability of the permeable membrane is in inverse
proportion to the thickness thereof such that the hydrogen flux
through a membrane having a thickness of 1 .mu.m is 10 times that
of a membrane having a thickness of 10 .mu.m, for example. When the
hydrogen flux is increased to 10 times, the surface area of the
membrane necessary for attaining the same hydrogen flux is reduced
to 1/10. When the thickness of the permeable membrane is reduced to
1/10, therefore, the necessary weight of the membrane is reduced to
1/100. According to the present invention, therefore, a dense
permeable membrane having excellent hydrogen permeability can be
formed with a thickness of not more than 1 .mu.m, whereby a compact
substance separation structure having high performance can be
prepared at a low cost.
When the surface of the porous base material is polished with
nonporous diamond grains, the hole portions of the porous base
material remain as cavities on the surface and hence the surface
roughness exceeds 1 .mu.m in Rmax. Consequently, the permeable film
of not more than 1 .mu.m in thickness cannot be formed on the
surface of the base material in a state with no pinholes.
When the porous layer is formed on the surface of the porous base
material having continuous holes by a sol-gel method or the like,
the mean thickness Ta of the portions A of the porous layer formed
in the holes of the base material is reduced below the mean
thickness Tb of the portions B of the porous layer formed on the
surface of the base material outside the holes. In other words, the
ratio (Tb/Ta) of the mean thickness Tb of the portions B to the
mean thickness Ta of the portions A exceeds 1. When the permeable
membrane is formed on the surface of the base material treated in
this manner, adhesion between the permeable membrane and the base
material is reduced. Therefore, the permeable membrane is separated
from the base material when purifying hydrogen-containing gas.
EXAMPLE 1
A porous silicon nitride sintered body having surface roughness of
about 2.0 .mu.m in Rmax was prepared as the base material for a
substance separation structure. A surface of the aforementioned
porous silicon nitride sintered body was polished with aluminum
oxide abrasive grains of 0.05 .mu.m in mean grain size, to be
flattened. The mean pore diameter of the porous silicon nitride
sintered body was 0.3 .mu.m. The aluminum oxide abrasive grains
contained 15 mass % of .alpha.-aluminum oxide grains and 85 mass %
of .gamma.-aluminum oxide grains. The polished porous silicon
nitride base material exhibited surface roughness of 0.3 .mu.m in
Rmax. The surface roughness was measured with a tracer type surface
roughness tester (measurement resolution: 0.01 .mu.m) provided with
a tracer having a radius R of 100 .mu.m on the forward end. The
ratio (Tb/Ta) of the mean thickness Tb of the portions B of the
aluminum oxide layer formed on the surface of the silicon nitride
base material outside the holes of the silicon nitride base
material to the mean thickness Ta of the portions A formed in the
holes of the silicon nitride base material was 0.1.
An arc ion plating apparatus was used for forming a permeable
membrane on the surface of the porous silicon nitride base material
treated in the aforementioned manner. Palladium was set on a target
in a chamber of the arc ion plating apparatus as the material for
the permeable membrane, at a distance of 300 mm from the base
material. The pressure in the chamber of the arc ion plating
apparatus was set to 2.66.times.10.sup.-3 Pa (2.times.10.sup.-5
Torr), and the arc ion plating apparatus was driven with a bias
voltage of -400 V and an arc current of 80 A. Thus, a palladium
film of 1.0 .mu.m in thickness was formed on the surface of the
base material.
No pinholes were observed on the surface of the obtained palladium
film. In this film, palladium crystals were oriented and grown on
(111) planes.
The substance separation structure prepared in the aforementioned
manner was employed for purifying hydrogen-containing gas at a
temperature of 500.degree. C. In this case, the palladium film was
not separated from the base material but maintained a dense state
with no pinholes. Thus, it was possible to remarkably suppress gas
other than hydrogen from passing through the hydrogen-permeable
membrane for obtaining high-purity gaseous hydrogen.
EXAMPLE 2
In order to form a permeable membrane on a surface of a porous
silicon nitride base material flattened similarly to Example 1, an
arc ion plating apparatus was driven for 10 minutes under the same
conditions as Example 1, except that the bias voltage was set to
-1000 V. Thus, a palladium film of 0.3 .mu.m in thickness was
formed on the surface of the base material.
No pinholes were observed in the surface of the obtained palladium
film. In this film, palladium crystals were oriented and grown on
(111) planes.
The substance separation structure prepared in the aforementioned
manner was employed for purifying hydrogen-containing gas at a
temperature of 500.degree. C. In this case, the palladium film was
not separated from the base material but maintained a dense state
with no pinholes. Thus, it was possible to remarkably suppress gas
other than hydrogen from passing through the permeable membrane for
obtaining high-purity gaseous hydrogen.
EXAMPLE 3
In order to form a permeable membrane on a surface of a porous
silicon nitride base material flattened similarly to Example 1, an
arc ion plating apparatus was driven for 10 minutes under the same
conditions as Example 1, except that a palladium-silver (Pd--Ag)
alloy containing 75 mass % of Pd and 25 mass % of Ag was set on the
target as the material for the permeable membrane. Thus, a
palladium-silver alloy film of 1.0 .mu.m in thickness was formed on
the surface of the base material.
No pinholes were observed in the surface of the obtained
palladiumsilver alloy film. In this film, crystals of the
palladium-silver alloy were oriented and grown on (111) planes.
The substance separation structure prepared in the aforementioned
manner was employed for purifying hydrogen-containing gas at a
temperature of 500.degree. C. In this case, the palladium-silver
alloy film was not separated from the base material but maintained
a dense state with no pinholes. Thus, it was possible to remarkably
suppress gas other than hydrogen from passing through the permeable
membrane for obtaining high-purity gaseous hydrogen.
EXAMPLE 4
A porous silicon nitride sintered body having surface roughness of
about 2.0 .mu.m in Rmax was prepared as the base material for a
substance separation structure. A surface of the aforementioned
porous silicon nitride sintered body was polished with aluminum
oxide abrasive grains of 0.05 .mu.m in mean grain size, to be
flattened. The mean pore diameter of the porous silicon nitride
sintered body was 0.3 .mu.m. The aluminum oxide abrasive grains
contained 15 mass % of .alpha.-aluminum oxide grains and 85 mass %
of .gamma.-aluminum oxide grains. The polished porous silicon
nitride base material exhibited surface roughness of 0.3 .mu.m in
Rmax. The surface roughness was measured with a tracer type surface
roughness tester (measurement resolution: 0.01 .mu.m) provided with
a tracer having a radius R of 100 .mu.m on the forward end. The
ratio (Tb/Ta) of the mean thickness Tb of the portions B of the
aluminum oxide layer formed on the surface of the silicon nitride
base material outside the holes of the silicon nitride base
material to the mean thickness Ta of the portions A of the aluminum
oxide layer formed in the holes of the silicon nitride base
material was 0.9.
In order to form a permeable membrane on the surface of the porous
silicon nitride base material treated in the aforementioned manner,
an arc ion plating apparatus was driven for 10 minutes under the
same conditions as Example 1. Thus, a palladium film of 1.0 .mu.m
in thickness was formed on the surface of the base material.
No pinholes were observed in the surface of the obtained palladium
film. In this film, palladium crystals were oriented and grown on
(111) planes.
The substance separation structure prepared in the aforementioned
manner was employed for purifying hydrogen-containing gas at a
temperature of 500.degree. C. In this case, the palladium film was
not separated from the base material but maintained a dense state
with no pinholes. Thus, it was possible to remarkably suppress gas
other than hydrogen from passing through the permeable membrane for
obtaining high-purity gaseous hydrogen.
COMPARATIVE EXAMPLE 1
A porous silicon nitride sintered body having surface roughness of
about 2.0 .mu.m in Rmax was prepared as the base material for a
substance separation structure. A surface of the aforementioned
porous silicon nitride sintered body was polished with diamond
abrasive grains of 0.25 .mu.m in mean grain size, to be flattened.
The mean pore diameter of the porous silicon nitride sintered body
was 0.3 .mu.m. The surface roughness of the polished porous silicon
nitride base material was 1.2 .mu.m in Rmax.
In order to form a permeable membrane on the surface of the porous
silicon nitride base material treated in the aforementioned manner,
an arc ion plating apparatus was driven for 10 minutes under the
same conditions as Example 2. Thus, a palladium film of 0.3 .mu.m
in thickness was formed on the surface of the base material.
Pinholes were present in the surface of the palladium film formed
in the aforementioned manner. Thus, it was impossible to form a
dense palladium film on the surface of the base material.
COMPARATIVE EXAMPLE 2
A porous silicon nitride sintered body having surface roughness of
about 2.0 .mu.m in Rmax was prepared as the base material for a
substance separation structure. In order to form a permeable
membrane on a surface of this porous silicon nitride base material,
an arc ion plating apparatus was driven for 10 minutes under the
same conditions as Example 2. Thus, a palladium film of 0.3 .mu.m
in thickness was formed on the surface of the base material.
Pinholes were present in the surface of the palladium film formed
in the aforementioned manner. Thus, it was impossible to form a
dense palladium film on the surface of the base material.
According to the present invention, as hereinabove described, a
compact substance separation structure having high hydrogen
permeability and durability can be prepared at a low cost.
Although the present invention has been described and illustrated
in detail, it is clearly understood that the same is by way of
illustration and example only and is not to be taken by way of
limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *